High-Q Superconducting Lumped-Element Resonators for Low-Mass Axion Searches

Low-frequency superconducting lumped-element resonators have recently attracted significant attention in the context of axion dark matter searches. Here we present the design and implementation of a fixed-frequency superconducting resonator operating near $250\mathrm{k}\mathrm{H}\mathrm{z}$, possessing an inductor volume of $\sim 1$ liter and achieving an unloaded quality factor $Q\approx 2.1\times {10}^6$. This resonator represents a significant improvement over the state of the art and informs the design of searches for low-mass axions.